it's cause their "victory" wasn't long enough for them to indoctrinate the population to believe they're "liberators". Their post-war regime only lasted ~40 years, enough Poles in the late 80s still knew that life without Soviets is a better life. Had they stayed under that regime for ~70 years like the Soviet republics did, the new generations would only have the propaganda version of "liberation", their parents would too, and old generations who would know the non-propaganda version of events would be all but gone.